Fog inhibitor for photographic emulsions



Patented May 16, 1939 UNITED STATES TE NT QFF [C E FOG INHIBITOR FOR;PHOTOGRAPHIC EMULSIONS i New Jersey No- Drawing. Originalapplication.,May. 7, 1936, Serial No. 78,464; Divided and thisapplication January 22, 1937, Serial No. 121,863

6' Claims.

This invention relates to fog inhibitors for photographic emulsions andto photographic emulsions containing them.

This application is a division of application Serial No. 78,464, filedMay 7, 1936.

It is known that photographic emulsions particularly ultra-sensitiveemulsions, or those con taining color sensitizers exhibit a tendency toforma deposit of silver in the emulsion. This deposit extends more orless uniformly over the entire emulsion and is known as fog.Photographic fog is of two types, local and general. Local. fogis'formed by exposure of the film or plate: at undesired points, as by alight leakv in the-.came'ra. General fog or; as it is sometimes known,chemical fog, is formed in. a number of ways. It may be caused by theconditions under which the film or plate is stored, such as conditionsof high temperature or unusually long time of storage. The nature of theemulsion, as where emulsions are highly sensitive may also producechemical fog, as 'well as the conditions of development of the emulsion,as by development'for protracted periods of time or at temperaturesabove normal. Highly sensitive emulsions are more likely tofog thanthose of lower sensitivity, owing to the small amount of energy requiredto make a silver halide grain developable. We are concerned primarilywith general or chemical fog.

The primary object of the present invention is to provide anti-foggingor fog inhibiting agents for ultra-sensitive photographic emulsions andto thereby increase the stability of the emulsions. A further object isto provide anti-fogging agents which do not markedly lower thesensitivity of the emulsion.

These objects are accomplished by incorporating in the emulsion analicyclic amine having at least two nuclei, each containing at least oneNH2 group. Either or both nuclei may be further substituted. The nucleimay be of the benzene or naphthalene type and the NI-Iz group may be ineither or in both of these nuclei. The nuclei may-be furthersubstituted, for example, with an alkyl group, or with two alkyl groups,or they may be unsubstituted except for the NHz groups.

These compounds are incorporated in a fast negative emulsion,particularly a silver halide emulsion. The emulsion used may be onewhich is intended to be used directly after 'emulsification or one whichis subjected to ripening by treatment at a high temperature or bytreatment with ammonia.

The first class of compounds which we may use includes benzidine and itsderivatives. These include benzidine, amino substituted derivatives. ofbenzidine, such as tetra-methyl benzidine; ring substituted derivativesof benzidine, such as-ortho-tolidine and dianisidine. of compounds whichwe contemplate using are the amino derivatives of diphenyl methane.These. include p:p'-diamino diphenyl methane; derivatives in which theamino group is substituted, such as tetra-methyl diamino diphenylmethane and p:p'-tetra-ethyl diamino diphenyl methane; ring substitutedderivatives, such as 2 :2 -4 z 4 -tetra-amino-5 -dimethyl diphenylmethane (sulfate).

In the diphenyl methane type of compound, which hasthe followingstructural. formula:

the CI-Iagroup between the rings may be replaced by other groups, suchas --(CH2)n-, S'-, -Q--.

In these compounds the benzene nucleus may be substituted by anaphthalene nucleus which may contain substituent groups in the ring, asdescribed above'for the benzene ring compounds. The compounds'describedabove do not all function equally well as fog inhibitors and difierentamounts are required to secure the maximum fog inhibiting effect. Thiseffect will depend to some extent on the type of emulsion used. Ingeneral, the amount of fog inhibiting agent used in the emulsion willvary from .01 gram to 5 grams per 1000 cos. of wet emulsion. Thefollowing table will serve to illustrate amounts which we have found tobe satisfactory. In each case the amount specified is used with 1000 cc.of a gelatino-silver halide emulsion.

Grams Benzidine 1 Tetra-methylbenzidine 1 o-Tolidine less than 1Dianisidine 1 p:p-Diaminodiphenylmethane 1Tetra-methyldiaminodiphenylmethane 1-5p:p-Tetra-ethyldiaminodiphenylmethane l-5 2 2'-4 4' -tetra-amino-55'-dimethyldiphenylmethane (sulfate) less than 1-5 The second class ingthem with any suitable solvent which is inert with respect to thesensitive emulsion, such as water, methyl alcohol, ethyl alcohol,acetone and others. The following example, which is by way ofillustration only, indicates methods of incorporating the anti-foggingagents in emulsions according to our invention.

Example I A gelatino-silver halide negative emulsion which containedsensitizing agent and which had been made in the usual way and had a pHof 7.4 was heated on a water bath sufficiently to melt it. To a 1000 cc.portion of this emulsion there were added 100 cos. of an ethyl alcoholsolution containing 1 gram of benzidine. The resulting solution wasthoroughly mixed and was coated on 'glass plates, dried and incubatedfor 7 days at 60 C. to obtain a fog test. The fogging produced at theend of this time was very much less than that produced on a plate coatedwith the emulsion to which no fog inhibiting agent had been added.

The fog inhibiting agents which we have described may be used in variouskinds of photographic emulsions. In addition to being useful in ordinarynon-color sensitized emulsions they may also be used in orthochromatic,panchromatic and X-ray emulsions. They may be used with or without colorsensitizing dyes and if used with the sensitizing dyes they may be addedto the emulsion before or after the dyes are added. Various silver saltsmay be used as the sensitive salt, such as silver bromide, silveriodide, silver chloride or mixtures of these. The dispersing agent maybe gelatin or other colloids, such as collodion, albumin, or suitablecellulose organic derivatives or artificial resins.

It is to be understood that we contemplate as included within ourinvention all modifications and equivalents coming within the scope ofthe appended claims.

What we claim and desire to secure by Letters Patent of the UnitedStates is:

1. A photographic emulsion comprising gelatin having a sensitive silversalt dispersed therein and containing as an antifoggant benzidine.

2. A photographic emulsion comprising gelatin having a sensitive silversalt dispersed therein and containing as an antifoggant ortho-tolidine.

3. A photographic emulsion comprising gelatin having a sensitive silversalt dispersed therein and containing as an antifoggant2:2'-4:4'-tetraamino-5:5-dimethyl diphenyl methane sulfate.

4. A photographic emulsion comprising gelatin having a sensitive silversalt dispersed therein and containing as an anti-foggant a compoundhaving the general formula wherein Y is selected from the groupconsisting of amino and alkylamino groups, and Z is selected from thegroup consisting of alkyl, oxalkyl, and hydrogen.

6. A photographic emulsion comprising gelatin having a. sensitive silversalt dispersed therein and containing as an anti-foggant a compoundhaving the general formula I Z Z wherein X is selected from the groupconsisting of sulfur, oxygen,'and (CI-I2)" where n is any whole number,T is selected from the group consisting of amino and alkylamino', Y isselected from the group consisting of amino, alkylamino, and hydrogen,and Z is selected from the group consisting of alkyl and hydrogen.

SAMUEL E. SHEPPARD.

WALDEMAR VANSELOW.

